Most shoes including athletic shoes employ a shape under the ball and toes of the wearer's foot which bends upward from the arch of the foot to the toe of the foot. This shape known as "positive rocker" allows the shoe to roll forward with the ball of the foot during normal walking or running motion. In most activities this is the natural motion of the foot and positive rocker provides the maximum comfort in wearing the shoe for extended periods. Wear on the sole of the shoe is also typically minimized by the positive rocker shape.
The composition and structure of the sole on many athletic shoes has been designed to provide cushioning of impact and resilience or rebound to store and release the energy absorbed by the sole during running, jumping or other similar activity.
The positive rocker of the shoe allows the sole and upper of the shoe to bend upwardly with the toes. Little or no mechanical support is provided by the shoe to assist the plantar muscles of the foot and the other flexor muscles in the lower calf of the leg which flex the toes and point the foot. If anything, the plantar muscles of the foot must work against the sole of the shoe in the direction flattening the sole which is the direction of force for launching the foot during running or walking.
High speed sprinting and high jumping or pole vaulting which are the ultimate extensions of athletic endeavors of this kind place significant strain on the muscles of the foot. The athlete employees the foot muscles as well as the muscles of the lower calf to launch the foot and as a result the leg and the remainder of the body from the ground. Normal track shoes for running or jumping provide only limited mechanical advantage. Energy absorbed in the resilient sole of most of these shoes is partially returned by the rebound of the material of the sole. However, the spring constant and length of compression are limited by the depth of the sole of the shoe. Consequently, conversion of the kinetic energy available from the foot striking the ground to potential energy stored in the sole of the shoe and then the reconversion to kinetic energy is severely limited.
Another sport requiring significant foot strength is rock climbing. The athlete engaged in a climb with a high degree of difficulty must rely on hand holds and toe holds which are very small. The toe hold is often engaged by only a very small part of the forward-most portion of the sole on the climbing boot. In a climbing boot employing positive toe rocker the boot tends to flex upwardly at the toe providing minimal support. The entire weight of the climber resting on the foot must therefore be supported by the plantar muscles of the foot and the flexor muscles for the foot located in the lower calf of the leg. The majority of these muscles are relatively small muscles in the human body and consequently are placed under great stress in this type of endeavor. Rock climbers often train with very light shoes having almost no sole called climbing slippers to strengthen the muscles required for high difficulty climbs.
The prior art approach to assisting the climber has been to stiffen the sole of the positive rocker climbing shoe to prevent the sole from bending upwardly thereby reducing somewhat the load on the climber's foot when stationary. However, in many situations the muscles in the climber's foot must not only support the climber's weight but work against the stiffened sole when the climber is extending upward for the next handhold or foothold. In addition increased stiffness in the sole reduces the amount of feeling or sensitivity the climber has in the foot to "feel" the foot hold in the rock.
Stiffening of the sole through harder materials or in mid-sole stiffeners made of metal or plastic also cause the boot to no longer conform to the foot unless the foot is in the initial position conforming to the boot. Further, since the boot is not flexible the boot will not conform to the foothold in the rock. Thereby adversely affecting the friction between the boot and the rock.
It is therefore desirable to provide a shoe which will offer a mechanical advantage to the athlete both in the form of energy conversion from kinetic to potential and back to kinetic and, in a static case, the transfer of force from the plantar muscles in the foot and flexor muscles of the calf, which control the toes, to the much larger calf muscles, the soleus and gastrocnemius which flex or point the foot as a whole.